We are studying the sequence organization, transcription, and control of Drosophila heat shock loci. These loci undergo rapid and intense activation following certain stimuli, including temperature elevation. We have cloned messenger and other sequences from the heat shock loci at 63BC 67B, 87A, 87C and 95D and are using a variety of biochemical, genetic and cytogenetic techniques to characterize the pattern of transcription and RNA processing and to identify sequences involved in controlling heat shock gene expression. Naturally occurring polymorphisms and species differences among D. simulans, melanogaster, mauritiana, and virilis will be used to study the regulation of heat shock gene expression, to test models for certain types of position effect and to discern possible rules of sequence evolution. Transcription of cloned heat shock sequences in vitro and in injected Drosophila cells will be attempted in order to test the effect of various sequence alterations on transcription. Hybridization in situ will be used to identify interbands associated with heat shock loci in polytene chromosomes in order to test models for interband sequences and structure.